PRONOMOTHERIUM 



169 



elongate finger-like process filled with cancellous tissue, somewhat after the manner of the Suicke. 

 The paroccipital processes are long and slender. The occipital condyles face mainly downward with 

 respect to the palatal plane. Index: 0.62. 



Fig. 121. — Pronomotherium siouense Sinclair. Superior view of skull. PLT. Cat. No. 18333 A.M.N.H. 2/5 nat. size. 



(Photograph from the American Museum.) 



Mandible: From the holotype it is discerned that the chin is steeply sloping, gently convex 

 transversely, and concave vertically. The contour of the inferior border of the ramus descends more 

 gradually, beginning under P 4 and curving continuously to its maximum under the posterior lobe of 



Fig. 122. — Pronomotherium siouense Sinclair. Inferior view of skull. PLT. Cat. No. 18333 A.M.N.H. 2/5 nat. size. 



(Photograph from the American Museum.) 



M 3 . In other words, it has not the sudden change in slope which characterizes P. altlramus and 

 P. laticeps. It has, however, the great posterior depth of this genus. The coronoid process is short 

 and slender; the sigmoid notch is shallow and wide open, and the masseteric fossa is small and 

 confined to the part lying above a line along the alveolar parapet. The condyle is not offset from 

 the ascending ramus and is gently concave fore and aft. 



